The Influence of Tungsten Alloying Additions on the Passivity of Aluminum

Abstract

Transition metals such as Mo, W, Ta, Cr, and W can be used to significantly enhance the localized corrosion resistance of A1. Since these elements exhibit very low solubilities in aluminum, a nonequilibrium alloying method, such as sputter deposition, must be used to produce single-phase alloys. The addition of approximately 9 atom percent W to A1 can shift its pitting potential in the positive direction as much as 2600 mV. Heat-treatment of these nonequilibrium alloys results in the precipitation of a second phase that is detrimental, but not catastrophic, to corrosion performance. Surface analysis of the AI-W passive film formed as a function of applied anodic potential reveals that it remains thin throughout the polarization sequence and contains very little oxidized solute, regardless of the applied potential. The oxidized W present in the film is in the form of WO2 and WO3 (or WOg2). Previously, it was proposed that the enhanced passivity for sputter-deposited A1-Mo, A1-Cr, and A1-Ta alloys was a result of the oxidized solute in the film (MoO~ 2, CrOOH, or Ta20~), making the film less susceptible to chloride attack by electrostatic-repulsion, oxide-structure modification, or oxidized-solute barrier-layer formation mechanisms. The results of this investigation reveal that the electrostatic-repulsion or oxidized-solute barrierlayer mechanisms are not responsible for the dramatic enhancement in the passivity of A1 with the addition of W. Instead, the small amount of oxidized W in the passive film may interact synergistically with the hydrated aluminum oxide structure to form a more protective film.

Electrodeposition of Al-W Alloy Films in a 1-Ethyl-3-methyl-imidazolium Chloride-AlCl3Ionic Liquid Containing W6Cl12

“…• C in the equilibrium state, 2 the formation of Al-W alloy films having high corrosion resistances requires non-equilibrium processes, such as sputtering, 1,[3][4][5][6][7][8] ion implantation, 9 and electrodeposition. [10][11][12] Of these methods, electrodeposition has particular advantages in that a uniform film can be formed relatively quickly and continuously, onto substrates having complex shapes, using simple equipment.…”

“…Reports on the electrodeposition of Al alloys including Al-Ni, 13 Al-Ti, 14 Al-V, 15 Al-Zr, 16 Al-Mo, 17 Al-Mn, 18 and Al-Hf 19 are available in the literature. A previous study revealed that electrodeposition in a EMIC-AlCl 3 bath with the addition of W(IV) chloride (WCl 4 ) yielded Al-W alloys, but the W content was lower than 1 at.%. 10 Recently, the electrodeposition of Al-W alloy films from an EMIC-AlCl 3 bath with the addition of the W(III) compound K 3 W 2 Cl 9 was reported.…”

“…• C. To electrodeposit dense Al-W alloy films with a high W content at a high current density, an effective approach is to use a W ion source that can dissolve in EMIC-AlCl 3 …”

X-ray Photoelectron Spectroscopic Study on the Anodic Passivity of Sputterdeposited W-Ta Alloys in 12 M HCl

“…Lee et al (1996Lee et al ( , 1997 reported a beneficial effect of tantalum to improve the corrosion resistance of nickelbase alloys in 12 M HCl. A series of the sputterdeposited binary tantalumcontaining alloys showed higher corrosion resistance than those of alloying elements due to spontaneous passivation in aggressive media (Shaw et al 1991, Yoshioka et al 1991, Kim et al 1994, El Moneim et al 1997.…”

Electrodeposition of Al-W-Mn Ternary Alloys from the Lewis Acidic Aluminum Chloride−1-Ethyl-3-methylimidazolium Chloride Ionic Liquid

“…Among the non-equilibrium binary alloys, it is well-known that Al-W prepared by the physical non-equilibrium alloying methods described above show the most anodic chloride-induced pitting corrosion potential. [20][21][22][23][24] When the W content of these alloys exceeds ca. 10 atomic percent (a/o), the passive region of the Al-W alloy extends to nearly +2,600 mV against pure aluminum.…”